The Research Of Flammable Ice Genetic Mechanism In The Permafrost

With resources of petroleum and natural gas in the world gradually exhausted, mankind will face a situation of dried-up oil-gas resources in the later 21st century, so it has become the aim of scientific community to seek clean and efficient new energy. Scientists of all countries are committed to find new replaceable energy and have continuously invested a great deal of capital and manpower into the research of new energy. Known as a strategic resource with commercial development potential in the 21st century, flammable ice is increasingly regarded by scientists and governments of all countries.Flammable ice has the characteristics of shallow burying, large scale, high energy density, cleanness, etc. and is a high-quality efficient fuel. It is generally thought in the scientific community that the flammable ice will eventually become the most potential future clean energy resource of mankind. The study of flammable ice involves not only the energy problem but also the related domains of environment, global climate change, subsea safety, natural gas transportation and solidification as well as national security, which are more important. Therefore, the study of flammable ice has become the hotspot and focus of scientists of all countries in the world. The finding of large-scale flammable ice reserves brings the study of hydrate into a new phase. The scientists of all countries in the world have conducted broad and efficient study on the type and physical properties of flammable ice, conditions for natural existence and mineralization, resource evaluation, ways of exploration and development as well as the relationship between gas hydrate and global change and marine geological disasters and have achieved remarkable results.Through collection of related information concerning the formation and decomposition of flammable ice, the article starts from the composition, structure and features of flammable ice, analyzes the structure, existence features, physical and chemical properties, origin of hydrate and model of geological structure of flammable ice and summarizes and analyzes the technical problems and environmental influence of exploiting flammable ice. Starting from the conditions for phase equilibrium of flammable ice, the article analyzes and summarizes the existing three basic methods of exploiting natural gas hydrate: thermal excitation method, pressure reducing method and inhibitor injection method, analyzes their advantages and disadvantages and proposes the feasibility of hot water-injection decomposition method. Starting from the hot water-injection exploitation method of thermal excitation method, the article divides the heated decomposition into three associated phases and discusses them in detail. Based on some assumed conditions, the article studies the hydrate decomposition foreland from the angle of mass transfer and momentum conservation in the hot water-injection decomposition area of hydrate, establishes the mathematical model of corresponding partial differential equation and discloses the dynamic and thermodynamic features of hydrate decomposition. The article considers the heated exploitation of flammable ice as heat transfer problem with movable boundary and establishes the heat conduction equation among temperature fields of decomposition area, hydrate area and boundary surface, namely energy conservation equation, so that the differential equation for heat conduction during the decomposition under thermal effect as well as the boundary conditions and initial conditions is established and the analytic solutions for positions of decomposition area, hydrate area and decomposition foreland during the hydrate decomposition in stratum for one-dimensional questions are obtained. Energy analysis is conducted in the decomposition area and hydrate area during the heated exploitation of natural gas hydrate and the formula for calculating the rate of hydrate decomposition, change law of decomposition foreland with time and formulae for calculating the thermal efficiency and energy efficiency of heated exploitation of natural gas hydrate are got to facilitate the economic evaluation of selection of different parameters for heated exploitation of natural gas hydrate.After the natural gas hydrate is decomposed, a multi-phase infiltration flow of water, gas and hydrate will be formed in the hydrate reservoir. The article establishes the mass conservation equation from the angle of field theory when hydrate is heated to decompose into water, gas and hydrate (namely infiltration flow equation, with law of infiltration flow consistent with Darcy's Law), other auxiliary equations as well as initial conditions and boundary conditions so as to establish the mathematical model of heated exploitation of hydrate and discusses related problems.